Furnace



.May 25, 1937. J. o. BETTERTON Er AL FURNACE Filed Aug. 14, 1934 2Sheets-Sheet 1 May 25, 1937. J. o. BETTERTON r AL FURNACE Filed Aug. 14,1934 Patented vMay 25, 1937 UNITED STATES .PATENT `OFFICE FURNACEApplication August 14,

13 Claims.

This invention relates to furnaces. 'I'he invention provides an improvedfurnace having a wide application in the chemical and metallurgical artsand is of particular importance in conducting volatilizing operations,especially those which are ordinarily effected only with difflculty. i

' Furnaces embodying the principles of the invention have, proved ofsignal importance in volatilizing a host of different compounds,materials and substances both pure and impure and in vaporizing and/orsubliming many of the oxides, suldes, chlorides, etc. of arsenic,antimony, cadmium, lead, selenium, tellurium, zinc and the like, as wellas various mixtures thereof. In such furnaces, remarkably improvedresults have been attained. Further, the invention permits suchreactions as oxidation, reduction, halogenation and sulphatization to bereadily practiced under precisely controlled conditions and any suchreaction can' be readily inaugurated to be continued indefinitely or, ifdesired, changed at will.

In accordance with the invention, a furnace is provided having means forsimultaneously heating atmosphere of'appropriate, controlled temperatureand desired chemical composition.

Although the novel features whichare believed to be characteristic ofthis invention will be particularly pointed out in the claims appendedhereto, the invention itself, as to its objects and advantages, and themanner in which'it may be carried out, may be better understood byreferring to the following description taken in connection with theaccompanying drawings forming a part thereof, in which Fig. 1 is' ,alongitudinal section through a furnace constructed `in accordance withthe invention,

Fig. 2 is a cross-section of the furnace shown in Fig, 1, taken alongthe line 2--2,

Fig. 3 is a section through a modified form of furnace embodying theinvention, and

Fig. 4f is-a section through a further modified form of furnaceembodying the invention.

In the following description and in theclaims, various details wi-ll beidentified by specific names for convenience, but they are intendedl tobe as generic in their application as the art will permit.

Referring now to4 Figs. 1 and 2, Athere is shown a furnace. of themuilied-iiame type having re tubes 'I0 and II extending from the burnerend of the furnace through a partition I2, which partition with end wallI3, defines chamber I4.

a charge and subjecting same to the action of an 1934, Serial No.739,720

Burn'ers I5 (one shown) are operatively associated with re tubes IIJ andII the latter being composed of silicon carbide and set in asbestoscement I6 at the burner end and a suitable highly refractory cement Ilin partition I2. Charge hoppers I8 and I9, equipped respectively withslide.

valves and 2|, open to the laboratory of the furnace 22 via feed ducts23 and 24 respectively. Gas-tight work door 25 permits access to thelaboratory of the furnace and a tap hole 26 equipped with removable plug21 is provided at the lowest point of hearth 28. Pyrometer 29 extendsthrough the side wall into the furnace laboratory. Positioned above thehearth of the furnace are inlet bale 30 and outlet baille 3I. Vent 32 ofchamber I4 is equipped with damper 33, and inspection door 34, samplingtube 35 equipped withpressure gauge 36, and auxiliary gas inlet 31 areprovided in wall I3. yPort 38 leads from chamber I4 to the laboratory ofthe furnace and outlet port 39 leads from the latter to the flue system40. i

In the modified form of furnace shown in Fig. 3 the laboratory of thefurnace is of increased dimension, the partition 4I serving both as anadditional baffle and as a support for the joint between re tubes 42 and43. In other respects the furnace structure is similar to that shown inFigs. 1 and 2 and the analogous parts are indicated by the referencecharacters bearing the suffix a. In the modified form shown in Fig. 4,

44 is` a kettle positioned over fire box 45 associated with burner 46and ue 41. The superstructure of the furnace is carried by steel members48' and 49 supported by I-beams' 50. Charge hopper 5I having screwconveyor 52 communicates with feed duct 53 via` slide valve- 54. Thekettle 44 and fire box 45 are suitably mounted (not shown) for raisingand lowering same into and out of operating position. In other respectsthe apparatus is similar to that shown in Figs. 1 and 2 as indicated bythe analogous reference characters bearing the suffix b.

In operation the material to be treated is placed in hoppers I8 and I9and supplied to the hearth of the furnace through feed ducts 23 and 24by suitable manipulation of slide valves 20 and 2I. Obviously thefeeding may be continuous or Iintermittent, the former, however, havingbeen found more advantageous for most operations involving the use ofthe furnace as a volatilizing unit. Suitable fuel is supplied by burnersI5 and burned in the fire tubes I0 and I I which produce a muiiled amefrom which the gases comprising the products of combustion passinto'chamber I4.

By suitable regulation, the composition of the combustion gases may beaccurately controlled over a Wide range from reducing through neutral tooxidizing. Further, their composition may be altered if necessary ordesirable by the introduc-4 -action is of vital importance as will belater pointed out. In order to leave the furnace, the gases must passunder exit baille 3| with the result that the moving gas stream sweepsthe charge during the entire duration of its passage through thelaboratory of the furnace. The sweeping gases then pass out of thefurnace through outlet port 39 into flue system 40 which may lead to abag filter or other suitable recovery apparatus.'

In the modification shown in' Fig. 3 an additional baille is provided toinsure the impingement of the sweeping gases upon the charge at alltimes during their passage through the furnace. In

Fig. 4 means for employing subsurface heating of the charge are shownwhich isvof advantage when working with some kinds of materials. Othermodifications may be made in the construction of the furnace Within theVscope o f the invention. For example, a false arch may be substitutedfor the re tubes as the combustion chamber and it is even possible tosubstitute electrical heating units and supply the sweeping gases froman outside source.

The efliciency of the improved furnace of the inventionis wellillustrated by the following comparative results obtained in thevolatilization of antimony trioxide. In one instance a prior art furnacewas used in which combustion gases were passed over the charge in theordinary manner and the rate of volatilization was found to be 'onepound per hour for each-square foot of hearth area. In two otherinstances a furnace was used which was heated by means of tubes ofsilicon carbide suspended in the upper part of the furnace laboratoryand the hot gases of combustion reversed and passed back through thelaboratory above the charge of impure antimony oxide. In both of thesecases the temperature was 900 C. but in the flrst'furnace which was notequipped lwith bailles the rate of volatilization was three 'area andthe product was only of fair quality.

In the second furnace, equipped with inlet and outlet baffles as shownin the drawings, the rate of volatilization was sixteen pounds per hourfor each square foot of hearth area and the product was of excellentquality.

It is believed that theimproved results attending the use of furnacesconstructed in accordance with the invention are to be attributed 'invthe main tothe heating of the charge by radiation while simultaneouslysweeping the charge with the gases in the manner shown. In volatilizingsubstances in such furnaces, abundantheat is radiated directly to thevery molecules passing from the condensed to the vapor state thusrendering the operation virtually independent of the high heatresistivity of surface films to convected,

heat which factor is the prime enigma of many of the prior art furnaces..At the same time, the

unique manner in which the combustion gases are jetted or impingedagainst the charge enables more heat to be extracted therefrom than whenthe gases are merely passed through the laboratory of the furnace.

It is well known that heat is absorbed wheny substances, for example,arsenious oxide or antimony oxide, are volatilized and the transmissionof heat from hot gases to a substance undergoing volatilization is morediicult than if the substance were substantially non-volatile. As theamount of heat of volatilization is of considerable magnitude, it isevident that unless sufficient heat can be constantly imparted to thesubstance, the rate of volatilization must necessarily be low. Inasmuchas furnaces in which the hot gases are simply passed through the furnacedo unquestionably give low rates of volatilization as compared to theimproved furnace of the invention, it is believed that the primaryreason for such low rates is due to inadequate transmission of heat duemainly to the difiiculty of causing convected heat to travel downwardlyin a furnace and to the fact that the Ivapors evolved from the chargeflow against'the invention provides many advantages in the treat-4 mentof a great variety of chemical and metallurgical substances. Whilecertain novel features of the invention have been disclosed and arepointed out in the annexed claims, it will be understood that variousomissions, substitutions and changes may be made by those skilled in thei port impinge upon the hearth of said main chamber.

2. In a furnace, a main chamber, re tubes positioned in the upperportion of said chamber interconnecting burners and a second chamber, aninlet port connecting said main and second chamber, an outlet portconnecting said main 'chamber-with a suitable ue system, bafflesassociated with said inlet and outlet ports for deflecting gases ontothe hearth of said chamber and an auxiliary gas inlet in saidsecondchamber.

I3. A furnace comprising a main furnace chamber having a hearth,charging means associated therewith, heating means in the upper portionof said chamber for burning fuel out of contact with the furnace charge,inlet and outlet ports inthe walls of said main chamber, baliles asso-.ciated with said ports and a second chamber adapted to receivecombustion gases from said heating means and supply them to the inletport.

4. In a furnace, a chamber having a solid hearth, inlet and outlet portsin the walls of said chamber, baffles associated with said ports,heating means for radiating heat to a charge on said hearth from fuelburned out of contact with said charge and means for circulatingcombusof said fire tubes, a port connecting said' main and secondchambers and a baiiie disposed in the travel of gases from said port fordirecting them downwardly onto saidcharge.

6. A furnace comprising a main furnace chamber, fire tubes positioned inthe upper portion of said chamber, a second chamber adapted to receivecombustion gases from said re tubes, means for supporting a charge inthe lower portion of'said chamber, an auxiliary heating appa; ratus forsupplying heat 'to the charge, an inlet port for supplying combustiongases from said second chamber to the charge, an exit port connectingsaid main chamber to a flue and baiiles associated with said inlet andoutlet ports to deect the combustion gases and cause same to sweep thecharge.

l said hearth to supply heat to the charge by radiation, means forreceiving the combustion gases and recirculating them through thelaboratory of the furnace and baffles positioned to jet the gasesagainst the charge yand sweep same during the entire passage of thegases through the laboratory of the furnace.

8. A furnace comprising a main chamber, a mixing chamber, re tubes insaid main'chamber and communicating with said mixing chamber, anauxiliary gas inlet associated with said mixing chamber, an inlet portconnecting said chambers, an outlet port leading from said main chamberto a fiue system and baffles in said main chamber so positioned thatgases passed through the main chamber via said ports are jetted againstthe charge in said main chamber.

9. A furnace comprising a main chamber, a mixing chamber, means forburning fuel out of contact with the charge in the main chamber the gasexit from said means terminating in said mixing chamber, an auxiliaryheatin'gelement for sub-surface heating of the charge in the mainchamber, an inlet port connecting said chambers,

an outlet port leading from the main chamber to a suitable flue andmeans in said main chamber for deecting and impinging gases passedthrough said main chamber via said ports against 4 the charge in saidmain chamber.

10. A furnace of the muflled-ame type comprising the combination with achamber defining a hearth for receiving a charge to be heated, ofburners for the furnace, refractory conduit associated with the burnersextending. through the hearth chamber of the furnace and'in the interior of which conduits combustion proceeds, an

auxiliary chamber communicating with the cons duits for receivingcombustion gases therefrom, means for the auxiliary chamber enabling thecomposition and temperature of the combustion gases to bepredeterminedly controlled and means for leading the said combustiongases from the auxiliary chamber into the hearth chamber.

11. A furnace of the muiiled-fiame type comprising ,the combination witha chamber having a hearth for receiving a charge of material to beheated, of an auxiliary chamber for receiving A v combustion gases, gasports interconnecting the auxiliary chamber with the hearth chamber,

` heating means for radiating heat to a charge on the hearth from fuelburned out of contact with the charge, means for -circulating combustiongases from the heating means into the auxiliary chamber and thence intothe hearth chamber through the said ports, and bafiies for directing theproducts of combustion into intimate contact with the charge on thehearth.

12. In the furnace treatment of volatile compounds, the improvementwhich comprises heat-v ing the charge predominantly with radiant heat byfuel burned out of contact with the charge and recirculating thecombustion gases back over the charge in such manner that they impingethereon thereby rapidly volatilizing the charge.

13. The process fortreating volatile substances vwhich comprisescharging the material to the` hearth of a furnace and heating thematerial predominantly by radiation while simultaneously andcontinuously impinging hot gases against lsubstantially the entiresurface of the charge whereby the material is volatilized at anextremely high rate.

JESSE O. BETTERTON. MELVILLE F. PERKINS.

